In-flight refueling (or air-to-air refueling) is an important method for extending the range of aircraft traveling long distances over areas having no feasible landing or refueling points. Tanker aircraft have been developed which have the capability of refueling a receiver aircraft while in flight. Tanker aircraft are typically converted cargo variants of large civil aircraft wherein at least one in-flight refueling device has been added such that aircraft fuel may be transferred from an internal and/or external tank carried by the tanker aircraft, via the in-flight refueling device, to a receiver aircraft while both the tanker and receiver aircraft are in flight.
There are currently two primary systems for in-flight refueling. One system is the boom refueling system. The boom refueling system typically comprises a rigid boom extending from a tanker aircraft. At one end of the boom is an in-flight refueling device comprising an extendable refueling tube wherein the extendable refueling tube is stowed concentrically within the boom and is further configured to telescope outward from the boom. Also disposed on the boom end are airfoils, which are controlled by a refueling system operator such as, for instance, a boom operator, onboard the tanker aircraft. The airfoils provide maneuverability of the boom with respect to a receiver aircraft. The operator of the receiver aircraft must maneuver the receiver aircraft to within an in-flight refueling position, below and aft of the tanker aircraft. Upon maneuvering into the in-flight refueling position, the boom operator onboard the tanker aircraft may control the airfoils to position the boom into a position relative to the second aircraft such that the boom operator may extend the extendable refueling tube into a refueling connection with a fuel receptacle disposed on the receiver aircraft. The mechanisms for extending and/or retracting the extendable refueling tube may include, for instance, electromechanical components, hydromechanical components, pulleys, cables, sprockets and/or chains.
Another type of refueling system is the probe and drogue system. In the probe and drogue system, an in-flight refueling device comprising an elongate hose is trailed behind the tanker aircraft. Attached at the end of the hose is a funnel-shaped drogue. The receiver aircraft is provided with a probe that is flown by its operator into the drogue such that the probe engages the end of the hose and thus comes into fluid communication therewith such that in-flight refueling may commence. In many cases, as the receiver aircraft contacts the drogue, the probe pushes the drogue forward such that slack is developed in the refueling hose that must be taken up by the probe and drogue system. The hose is typically stored on a rotating drum housed within the fuselage of the tanker aircraft or an externally-mounted pod such that the hose may be reeled out to its trailing position behind the tanker aircraft and reeled back in to take up slack in the refueling hose and/or stow the refueling hose at the conclusion of an in-flight refueling operation. The mechanisms for extending and/or retracting the hose and drogue may include, for instance the drum assembly, electric and/or hydraulic motors, tension sensors for sensing tension levels in the refueling hose, and pressure sensors for determining fuel flow in the refueling hose.
For both types of in-flight refueling systems, the extension and retraction of a refueling device (a drogue in the hose and drogue system and an extendable refueling tube in the boom system) is actuated by electromechanical, and or hydromechanical systems that are subject to wear and may require substantial maintenance in order to be kept in proper working order. In addition, the various drum and mechanical reel components utilized to stow the refueling hose in the probe and drogue refueling system require a large amount of space to be carried by a tanker aircraft, thereby taking up cargo space that would otherwise be available within the tanker aircraft, as well as limiting the types of aircraft that may serve as tanker aircraft.
Therefore, there exists a need for an in-flight refueling system and method for extending and retracting in-flight refueling devices, such as, for instance, the refueling hose and attached drogue and the extendable refueling tube used in the boom in-flight refueling system, wherein the in-flight refueling system is robust, requires a minimum number of moving mechanical parts, and may be suited for installation in a variety of different configurations to be carried by various types of tanker aircraft. In addition, there exists a need for an in-flight refueling system that provides a more compact alternative to the rotating drum currently used to extend and retract the refueling hose and attached drogue used in probe and drogue refueling systems.